Most yo-yos are in the form of two disk-shaped side members that are connected to each other by some form of axle structure. The side members are typically made of plastic, metal or wood. The axle structure may be an assembly of multiple parts, or merely be in the form of a dowel or a riveted pin, and may be made of metal and/or wood and/or plastic. In many modern yo-yos, the axle structure includes a center-located bearing or other member that is secured to, and rotatable on, an elongated axle member.
The axle structure also forms an anchor for one end of a string-type tether. This is accomplished by having the tether's end-located loop encircle a portion of the axle structure.
The free end of the tether is usually tied to create a loop. This loop is normally placed about one of a user's fingers to thereby secure the yo-yo to the user. When the tether is wound about the axle structure and the yo-yo is released from the user's hand, the yo-yo will begin to rapidly spin as it moves away from the user's hand and the tether unwinds from the axle structure. Once the tether is fully unwound, the yo-yo may “sleep” at the end of the tether, whereby the yo-yo continues to spin without the tether rewinding on the axle structure.
There are three crucial performance characteristics of a yo-yo that enable a user to perform yo-yo tricks. The yo-yo must be capable of sleeping for an extended period of time, it should return on command, and it should be smooth on the tether.
Concerning a yo-yo's sleep time, the longer the yo-yo can be made to sleep, the more time the user will have to complete any particular yo-yo trick. It is well known that by minimizing friction in the yo-yo's components, one can maximize the yo-yo's sleep time.
For a yo-yo to return on command, the structure and design of the yo-yo must be such that when a user causes the tether to briefly go slack, a portion of the tether can snag a tether engagement member located on a spinning portion of the yo-yo. Tether engagement members, also herein referred to as engagement members, are any adaptations in the tether-facing surface of the yo-yo's side members designed to snag a portion of the yo-yo's tether. It should be noted that a tether-facing surface of a side member is herein defined as the surface of the side member that is normally oriented substantially perpendicular to the yo-yo's axis of rotation and that faces a portion of the yo-yo's tether at all times.
Concerning a yo-yo's ability to be smooth on the tether, this refers to a yo-yo's ability to be temporarily placed on a middle portion of the tether during a yo-yo trick and not have the tether inadvertently snag a spinning portion of the yo-yo. If the tether snags a spinning portion of the yo-yo at the wrong moment, the yo-yo will immediately return to the user's hand and the trick will be ruined.
The tendency of the tether to inadvertently snag on a spinning portion of the yo-yo is affected by a number of factors, including the size of the yo-yo's string gap and the aggressiveness of the yo-yo's tether engagement members. A yo-yo's string gap is herein defined as the open area between the yo-yo's two side members.
The width of the string gap is one of the most crucial elements in a yo-yo's design. The larger the width of the string gap proximate the axle structure, the further the tether has to travel before it can snag on a spinning portion of either of the yo-yo's side members. Too wide a string gap may preclude a user's ability to cause the tether to snag on a spinning portion of the yo-yo, with the result that a user cannot make the yo-yo return to his or her hand.
The aggressiveness of a yo-yo's tether engagement system is a measure of how readily the yo-yo's tether engagement members will snag a portion of the tether. While the tether engagement members facilitate the yo-yo's return on command, they are also usually responsible when the yo-yo inadvertently returns during a yo-yo trick. There is usually an inverse relation between the aggressiveness of the engagement system and a yo-yo's sleep time and smoothness on the string. Conversely, there is usually a direct relation between the aggressiveness of a yo-yo's engagement system and how easy it is for a user to get the yo-yo to return on command.
It has been a common practice in the yo-yo industry to provide different yo-yos for different types of users. A yo-yo designed for a beginner will often feature an aggressive tether engagement system, thereby favoring ease of return over all other performance characteristics of the yo-yo. It is thought that a beginning yo-yo player will have a more enjoyable experience if he or she can easily get the yo-yo to return on command. The player can then rapidly improve his or her skills with the yo-yo, until eventually the player may desire a yo-yo that is designed to favor other performance characteristics.
Higher performance yo-yos will often include adaptations that enhance sleep time and smoothness on the string. For example, while a ball bearing yo-yo can sometimes be harder to get to return than a fixed axle yo-yo, it will usually sleep longer on the end of a tether than most other yo-yos. Similarly, various tether engagement systems have been designed for the “pro” player and provide recessed or specially adapted engagement members that form a much less aggressive engagement system than the more common systems that employ a starburst shaped array of fixed engagement members that extend toward the yo-yo's tether.
Some modern yo-yos include an axle structure that enables a user to adjust the yo-yo's string gap. With these yo-yos, one can adjust the yo-yo to have a narrow string gap that facilitates a yo-yo's ability to return on command, or a wide string gap that favors a yo-yo's smoothness on the tether. However, with these yo-yos, there is no easy way to visually discern how a yo-yo will respond without actually trying the yo-yo. To adjust the yo-yo's responsiveness, a user will usually rotate one side member relative to the other by a small amount and then use the yo-yo once or twice to determine its responsiveness. This must often be repeated a number of times, requiring significant time and effort, before the yo-yo's responsiveness will be acceptable to the user. Furthermore, it often requires significant loosening of the yo-yo, up to two full turns of one of the yo-yo's side members, to go from a yo-yo condition in which return on command is favored, to a condition where the yo-yo is smooth on the string.